Eukaryotic bHLH/PAS (basic helix-loop-helix/Per-ARNT-Sim) transcription factors play a critical role in regulating cellular responses to hypoxia, xenobiotic compounds, and several other environmental conditions. Deregulation of these pathways is highly correlated with several forms of cancer, including solid tumor onset and progression, making their control of particular interest. To this end, the PAS domains within these factors represent particularly attractive targets for small molecule regulation given the role that these domains play as cofactor-regulated protein/protein interaction domains in a wide range of sensory proteins throughout biology. Here we propose the development of an HTS-compatible protein/protein interaction screen to identify compounds that can disrupt the complex between the PAS-B domain of ARNT (aryl hydrocarbon nuclear receptor translocator), a common element of several bHLH/PAS heterodimeric complexes, and coiled-coil segments of several coactivator proteins that are essential for ARNT function. Preliminary low-throughput assays suggest that this approach is feasible for conversion to HTS format, and a combination of in vitro biophysical and cell-based biochemical assays are already in place to validate compounds found in this manner. PUBLIC HEALTH RELEVANCE: We propose to develop an assay for high-throughput screening of small molecule disruptors of interactions between the ARNT/AINT transcriptional activator/coactivator pair. Inappropriate deregulation of this pathway is correlated with a variety of cancers, and the use of this assay to identify artificial compounds which can disrupt this complex will provide novel research tools for the study and manipulation of this complex.